Todays lecture objectives:

1
ATMS 305 Skew-T Log-P Indices

• Todays lecture objectives
• Skew-T Log-P Indices
• Will a thunderstorm happen today?
• If so, will it be severe?

?
2
ATMS 305 Skew-T Log-P Indices

• Todays lecture topics
• Skew-T Log-P Indices
• Upper air observations
• Details of the Skew-T Log-P Diagram
• Weather features on the Skew-T Log-P
• Useful parameters
• Stability indices

3
Skew-T Log-P
(courtesy F. Remer)
4
Upper Air Observations

• Radiosondes Measure
• Temperature
• Relative Humidity
• Wind Direction and Speed
• Pressure
• Height

(courtesy F. Remer)
5
Upper Air Observations

• Radiosonde Data Is Plotted on Charts
• Manual Analysis
• Plotting Done by Hand
• Computational Analysis Performed Graphically

(courtesy F. Remer)
6
Upper Air Observations

• Radiosonded Data Is Plotted on Charts
• Computer Analysis
• Plotting and Analysis Done by Computer

(courtesy F. Remer)
7
Rawinsonde (RAOB) Code

• Information is coded
• Data Transmission
• Data Storage

(courtesy F. Remer)
8
Skew T Log p Diagram

• Data can be plotted on thermodynamic diagrams
• TTAAs, TTBBs PPBBs

(courtesy F. Remer)
9
Skew-T Log-P

• Coordinates
• Pressure Decreases Logarithmically
• Temperature skewed _at_ 45o angle
• Easier to identify stable layers

(courtesy F. Remer)
10
Pressure
200
300
Pressure (mb)
400
500
600
700
800
900
1000
(courtesy F. Remer)
11
Temperature
(courtesy F. Remer)
12
Dry Adiabats

• Dry Adiabatic Lapse Rate

• Also Constant Potential Temperature

(courtesy F. Remer)
13
Dry Adiabats
-30
-40
-20
-50
-60
200
117
-10
107
300
97
0
87
Pressure (mb)
400
10
20
500
30
77
600
40
67
700
57
800
900
-23
-13
-3
7
17
27
37
47
1000
(courtesy F. Remer)
14
Pseudoadiabats

• Lines of constant saturated adiabatic lapse rate
• For saturated processes

(courtesy F. Remer)
15
Pseudoadiabats
(courtesy F. Remer)
16
Pseudoadiabats

• Equivalent Potential Temperature (qe)
• The potential temperature a parcel of air would
  have if all of its water vapor were condensed and
  the latent heat released warmed only the dry air.

(courtesy F. Remer)
17
Pseudoadiabats

• Equivalent Potential Temperature (qe)
• A measure of the total energy of a parcel of air.
• Conserved (or constant) for saturated adiabatic
  processes.

(courtesy F. Remer)
18
Pseudoadiabats

• Pseudoadiabats are also lines of constant
  Equivalent Potential Temperature (qe)

(courtesy F. Remer)
19
Pseudoadiabats
(courtesy F. Remer)
20
Pseudoadiabats

• Parallel to dry adiabats after water vapor has
  condensed out.

(courtesy F. Remer)
21
Pseudoadiabats
-30
-40
-20
-50
-60
200
-10
300
0
Pressure (mb)
400
10
20
500
30
600
40
700
800
2
5
9
14
17
22
25
30
900
1000
(courtesy F. Remer)
22
Mixing Ratio

• Conserved (or constant) for dry adiabatic ascent

mv
mv
(courtesy F. Remer)
23
Mixing Ratio
20
16
12
8
5
3
2
1
.4
(courtesy F. Remer)
24
Rawinsonde

• Measures
• Temperature
• Pressure
• Dew Point Depression
• Wind Speed Direction

(courtesy F. Remer)
25
Environmental Temperature
(courtesy F. Remer)
26
Dew Point
(courtesy F. Remer)
27
Temperature Inversion

• Increase in temperature with height

Inversion
(courtesy F. Remer)
28
Temperature Inversion

• Types
• Subsidence
• Frontal
• Radiation
• Turbulent

Inversion
(courtesy F. Remer)
29
Temperature Inversions
Radiation Inversion
(courtesy F. Remer)
30
Temperature Inversions
Frontal Inversion
(courtesy F. Remer)
31
Temperature Inversions
Subsidence Inversion
(courtesy F. Remer)
32
Clouds

• Temperature Dew Point Spread
• Less Than 5oC

(courtesy F. Remer)
33
Clouds
Clouds
(courtesy F. Remer)
34
Freezing Level

• Height at which 0oC occurs in the atmosphere

0oC
Freezing Level
(courtesy F. Remer)
35
Freezing Level

• Multiple Freezing Levels

0oC
Freezing Levels
(courtesy F. Remer)
36
Freezing Level

• Important in forecasting type of precipitation

SGF
LZK
JAN
(courtesy F. Remer)
37
Freezing Level

• Important in forecasting type of precipitation

SGF
0oC
Snow
(courtesy F. Remer)
38
Freezing Level

• Important in forecasting type of precipitation

LZK
0oC
Freezing Rain or Ice Pellet
(courtesy F. Remer)
39
Freezing Level

• Important in forecasting type of precipitation

JAN
0oC
Rain
(courtesy F. Remer)
40
Tropopause

• Top of Troposphere
• Lowest height at which the lapse rate decreases
  to 2oC per km or less

(courtesy F. Remer)
41
Tropopause

• Troposphere
• Temperature decreases with height
• Stratosphere
• Temperature increases with height

1
40
Pressure (mb)
10
Altitude (km)
Stratosphere
20
100
Tropopause
Troposphere
0
1000
-100 -80 -60 -40 -20 0 20 40
60
Temperature (C)
(courtesy F. Remer)
42
Tropopause
Tropopause
(courtesy F. Remer)
43
Tropopause

• Height
• Depends on Latitude
• Lower at Poles
• Higher at Equator

20
Tropopause
15
Tropopause
10
Tropopause
Altitude (km)
Tropical
Polar
Midlatitudes
5
0
Temperature
(courtesy F. Remer)
44
Tropopause

• Temperature
• Depends on Latitude
• Warmer at Poles
• Colder at Equator

20
Tropopause
15
Tropopause
10
Tropopause
Altitude (km)
Tropical
Polar
Midlatitudes
5
0
Temperature
(courtesy F. Remer)
45
Mixing Ratio (w)
-30
-40
-20
-50
-60
200
w _at_ 700 mb 2.5 g/kg
-10
300
0
Pressure (mb)
400
10
20
500
30
600
w
40
700
800
20
16
12
8
5
3
2
1
.4
900
1000
(courtesy F. Remer)
46
Saturation Mixing Ratio (ws)
-30
-40
-20
-50
-60
200
ws _at_ 700 mb 13 g/kg
-10
300
0
Pressure (mb)
400
10
20
500
30
600
40
ws
700
800
20
16
12
8
5
3
2
1
.4
900
1000
(courtesy F. Remer)
47
Relative Humidity (RH)
-30
-40
-20
-50
-60
200
RH _at_ 700 mb w/ws x 100 RH 2.5/13 x 100 19
-10
300
0
Pressure (mb)
400
10
20
500
30
600
40
700
800
20
16
12
8
5
3
2
1
.4
900
1000
(courtesy F. Remer)
48
Potential Temperature (q)
-30
-40
-20
-50
-60
200
117
q _at_ 700 mb 44oC 317K
-10
107
300
97
0
87
Pressure (mb)
400
10
20
500
30
77
600
40
67
700
57
800
900
-23
-13
-3
7
17
27
37
47
q
1000
(courtesy F. Remer)
49
Wet Bulb Temperature (Tw)
-30
-40
-20
-50
-60
200
Tw _at_ 700 mb 1oC
-10
300
0
Pressure (mb)
400
10
20
500
30
600
40
700
Tw
800
900
1000
(courtesy F. Remer)
50
Wet Bulb Potential Temperature (qw)
-30
-40
-20
-50
-60
200
qw _at_ 700 mb 14oC 287K
-10
300
0
Pressure (mb)
400
10
20
500
30
600
40
700
800
900
qw
1000
(courtesy F. Remer)
51
Equivalent Temperature (Te)
-30
-40
-20
-50
-60
200
Te _at_ 700 mb 20oC 293K
-10
300
0
Pressure (mb)
400
10
20
500
30
600
40
700
Te
800
900
1000
(courtesy F. Remer)
52
Equivalent Potential Temperature (qe)
-30
-40
-20
-50
-60
200
qe _at_ 700 mb 50oC 323K
-10
300
0
Pressure (mb)
400
10
20
500
30
600
40
700
800
900
qe
1000
(courtesy F. Remer)
53
Auto-Convective Ascent

• Air becomes buoyant by contact with warm ground
• Usually microscale or mesoscale

Hot
Cool
Cool
(courtesy F. Remer)
54
Auto-Convective Ascent

• Type of Clouds
• Cumulus

(courtesy F. Remer)
55
Auto-Convective Ascent

• Convective Condensation Level (CCL)
• the height to which a parcel of air, if heated
  sufficiently from below, will rise adiabatically
  until it is just saturated

CCL
(courtesy F. Remer)
56
Auto-Convective Ascent

• Convective Condensation Level (CCL)
• the height of the base of cumuliform clouds which
  are produced by thermal convection from surface
  heating

CCL
(courtesy F. Remer)
57
Convective Condensation Level (CCL)
CCL
Constant Mixing Ratio
Td
(courtesy F. Remer)
58
Auto-Convective Ascent

• Convective Temperature (Tc)
• the surface temperature that must be reached to
  start the formation of convective clouds by solar
  heating

CCL
Tc
(courtesy F. Remer)
59
Convective Temperature (Tc)
CCL
Constant Mixing Ratio
Dry Adiabat
Tc
Td
(courtesy F. Remer)
60
Auto-Convective Ascent

• Forecasting
• Will the afternoon temperature exceed the
  convective temperature?

NO!

• Thermals will form, but will not rise high enough
  to condense.

TltTc
(courtesy F. Remer)
61
Auto-Convective Ascent

• Forecasting
• Will the afternoon temperature exceed the
  convective temperature?

CCL
YES!

• Thermals will rise high enough to condense.

TgtTc
(courtesy F. Remer)
62
Forced Ascent

• Some mechanism forces air aloft
• Usually synoptic scale feature

Cold air
Warm air
Cool Air
(courtesy F. Remer)
63
Forced Ascent

• Type of clouds
• Depends on stability

Stable - Stratus Unstable - Cumulus
(courtesy F. Remer)
64
Forced Ascent

• Lifting Condensation Level (LCL)
• the height at which a parcel of air becomes
  saturated when it is lifted dry adiabatically

(courtesy F. Remer)
65
Lifting Condensation Level (LCL)
Constant Mixing Ratio
LCL
Dry Adiabat
Td
T
(courtesy F. Remer)
66
Forced Ascent

• Level of Free Convection (LFC)
• the height at which a parcel of air lifted dry
  adiabatically until saturated and
  pseudoadiabatically thereafter would first become
  warmer (less dense) than the surrounding air

(courtesy F. Remer)
67
Level of Free Convection (LFC)
Pseudoadiabat
Tpgt Te
Level of Free Convection
Tplt Te
Constant Mixing Ratio
LCL
Dry Adiabat
Td
T
(courtesy F. Remer)
68
Forced Ascent

• Equilibrium Level (EL)
• the height where the temperature of a buoyantly
  rising parcel again becomes equal to the
  temperature of the environment

(courtesy F. Remer)
69
Equilibrium Level (EL)
Tplt Te
Equilibrium Level
Tp Te
Tpgt Te
Level of Free Convection
Tplt Te
Constant Mixing Ratio
LCL
Dry Adiabat
Td
T
(courtesy F. Remer)
70
Positive Negative Areas
-30
-40
-20
-50
-60
200
Equilibrium Level
-10
300
0
Positive Area
Pressure (mb)
400
10
20
500
30
Level of Free Convection
600
40
700
LCL
800
900
Td
T
1000
(courtesy F. Remer)
71
Positive Negative Areas
-30
-40
-20
-50
-60
Negative Area
200
Equilibrium Level
-10
300
0
Pressure (mb)
400
10
20
500
30
Level of Free Convection
600
40
700
LCL
Negative Area
800
900
Td
T
1000
(courtesy F. Remer)
72
Maximum Parcel Level (MPL)
Max Parcel Level
-30
-40
Tplt Te
-20
-50
-60
200
Equilibrium Level
-10
Tp Te
300
Positive Negative
0
Pressure (mb)
400
10
Tpgt Te
20
500
30
Level of Free Convection
600
40
700
Tplt Te
LCL
800
900
Td
T
1000
(courtesy F. Remer)
73
Stability Indices

• Single number that characterizes the stability
  (or instability) of the atmosphere

5
15
7
22
1000
(courtesy F. Remer)
74
Stability Indices

• Advantages
• Ease of computation
• Easily used in forecasting
• Disadvantage
• Details of atmospheric profile may be ignored

(courtesy F. Remer)
75
Stability Indices

• Indices must be used with other forecasting
  methods
• Individual soundings must be examined closely

(courtesy F. Remer)
76
Showalter Index (SI)
-30
-40
-20
-50
-60
200
-10
300
0
Pressure (mb)
400
10
20
500
30
600
40
700
T
Td
800
850 mb
900
1000
(courtesy F. Remer)
77
Showalter Index (SI)
-30
-40
-20
-50
-60
200
-10
Pseudoadiabat
300
0
Pressure (mb)
400
10
20
500 mb
Tp
Te
500
30
600
LCL
40
700
T
Td
800
850 mb
900
1000
(courtesy F. Remer)
78
Showalter Index (SI)
-30
-40
-20
-50
-60
200
-10
Pseudoadiabat
300
0
Pressure (mb)
400
10
20
500 mb
-8oC
-10oC
500
30
600
LCL
40
700
T
Td
800
850 mb
900
1000
(courtesy F. Remer)
79
Showalter Index (SI)
(courtesy F. Remer)
80
Showalter Index (SI)

• Temperature and moisture at 850 mb may not be
  representative of conditions in boundary layer
• Good for mid-level convection

(courtesy F. Remer)
81
Lifted Index (LI)

• Addresses the limitations of the Showalter Index
• Accounts for boundary layer moisture

(courtesy F. Remer)
82
Lifted Index (LI)

• Variants
• Best Lifted Index
• Model Lifted Index

(courtesy F. Remer)
83
Lifted Index (LI)

• The temperature difference between
• the environmental air at 500 mb and
• the temperature of an air parcel at 500 mb
• first lifted dry adiabatically until saturated
  and then
• pseudoadiabatically from that level upward

(courtesy F. Remer)
84
Lifted Index (LI)
Forecast Maximum Temperature
Average Mixing Ratio Lowest 100 mb
(courtesy F. Remer)
85
Lifted Index (LI)
LCL
Dry Adiabatic
(courtesy F. Remer)
86
Lifted Index (LI)
Pseudo-adiabat
LCL
Dry Adiabatic
(courtesy F. Remer)
87
Lifted Index (LI)
Pseudo-adiabat
-6oC
-10oC
LCL
Dry Adiabatic
(courtesy F. Remer)
88
Lifted Index (LI)

• Lifted Index (LI)
• Positive - Stable
• Negative - Unstable

(courtesy F. Remer)
89
Lifted Index (LI)
(courtesy F. Remer)
90
(courtesy F. Remer)
91
K Index (KI)

• Measure of thunderstorm potential based on
• Vertical temperature lapse rate
• Moisture content of the lower atmosphere
• Vertical extent of the moist layer

(courtesy F. Remer)
92
K Index (KI)
Vertical Temperature Lapse Rate
Moisture Content of Lower Atmosphere
Vertical Extent of Moist Layer
T850 850 mb Temperature T500 500 mb
Temperature
Td850 850 mb Dew Point Temperature (T-Td)700
700 mb Dew Point Depression
(courtesy F. Remer)
93
K Index (KI)

• Does not require a plotted sounding
• Biased towards air mass type thunderstorms
• Works best for non-severe thunderstorms

(courtesy F. Remer)
94
K Index (KI)
(courtesy F. Remer)
95
Total Totals (TT)

• Used in identifying areas of potential
  thunderstorm development
• Sum of two other indices
• Vertical Totals (VT)
• Cross Totals (CT)

(courtesy F. Remer)
96
Total Totals (TT)
Total Totals
Vertical Totals
Cross Totals
T850 850 mb Temperature T500 500 mb
Temperature
Td850 850 mb Dew Point Temperature
(courtesy F. Remer)
97
Vertical Totals (VT)
T850 850 mb Temperature
T500 500 mb Temperature

• Lapse rate between 850 500 mb
• VT gt 26 for thunderstorm development
• Good for air mass thunderstorms
• Requires evaluation of moisture

(courtesy F. Remer)
98
Vertical Totals (VT)
(courtesy F. Remer)
99
Cross Totals (CT)
Td850 850 mb Dew Point Temperature
T500 500 mb Temperature

• Indicators of thunderstorm development
• High low level moisture
• Cold temperatures aloft
• CT gt 18 for thunderstorm development

(courtesy F. Remer)
100
Total Totals (TT)
Total Totals
Vertical Totals
Cross Totals

• More reliable predictor of severe thunderstorm
  activity
• Threshold values vary geographically

(courtesy F. Remer)
101
Total Totals (TT)
(courtesy F. Remer)
102
Severe Weather Threat Index (SWEAT)

• Estimate of severe weather potential
• Developed by USAF
• Five terms
• Low level moisture
• Instability
• Low level jet stream
• Warm air advection

(courtesy F. Remer)
103
Severe Weather Threat Index (SWEAT)

• Low Level Moisture
• 850 mb dew point
• Instability
• Total Totals
• Low Level Jet Stream
• 850 mb wind speed
• Warm air advection
• Veering wind between 850 mb and 500 mb

(courtesy F. Remer)
104
Severe Weather Threat Index (SWEAT)
Td850 850 mb Dew Point Temperature TT Total
Totals ff850 850 mb Wind Speed ff500 850 mb
Wind Speed dd850 850 mb Wind Direction dd850
850 mb Wind Direction
(courtesy F. Remer)
105
Severe Weather Threat Index (SWEAT)

• No term may be negative
• Td850 0 if negative
• 20(TT-49) 0 if TT is less than 49

(courtesy F. Remer)
106
Severe Weather Threat Index (SWEAT)

• 125sin(dd500-dd850).02 0 if any of the
  following conditions are not met
• dd850 is in the range 130o to 250o
• dd500 is in the range 210o to 310o
• dd500-dd850 gt 0
• ff850 and ff500 gt 15 kts

(courtesy F. Remer)
107
Severe Weather Threat Index (SWEAT)

• Estimate of severe weather potential
• Five terms
• Low level moisture
• Instability
• Low level jet stream
• Warm air advection

(courtesy F. Remer)
108
Severe Weather Threat Index (SWEAT)
(courtesy F. Remer)
109
Severe Weather Threat Index (SWEAT)

• Only indicates potential of severe weather
• Trigger needed to realize potential
• Includes shear term for severe thunderstorms

(courtesy F. Remer)
110
Convective Inhibition (CIN)

• Energy required to make a parcel buoyant
• The area (below the LFC) between the
  environmental sounding and the
• Dry adiabat if unsaturated
• Pseudo adiabat if saturated

(courtesy F. Remer)
111
Convective Inhibition
Level of Free Convection
CIN
LCL
Td
T
(courtesy F. Remer)
112
Convective Inhibition (CIN)

• Early Development of Convection
• 10 m2s2
• Squall Lines
• 50 m2s2
• No Thunderstorms (Capped)
• 150 m2s2

(courtesy F. Remer)
113
Convective Available Potential Energy (CAPE)

• Buoyantly Energy
• The area (above the LFC) between the
  environmental sounding and the pseudoadiabat

(courtesy F. Remer)
114
Convective Available Potential Energy (CAPE)
CAPE
Level of Free Convection
LCL
Td
T
(courtesy F. Remer)
115
Convective Available Potential Energy (CAPE)

• Unlikely Development of Strong Convection
• lt1000 J kg-1
• Strong or Severe Thunderstorms
• 2000 J kg-1

(courtesy F. Remer)
116
(courtesy F. Remer)
117
Maximum Temperature

• Assumes
• No significant temperature advection
• Strong winds not forecast

(courtesy F. Remer)
118
Maximum Temperature

• Clear or Scattered Sky
• Solar Radiation Mixes Boundary Layer

850 mb
Surface
Tmax
(courtesy F. Remer)
119
Maximum Temperature

• Broken or Overcast Sky
• Pseudo-adiabat

850 mb
Surface
Tmax
(courtesy F. Remer)
120
(No Transcript)